Think of iPhone as a little computer, even though Apple doesn't want you to. It has a processor, RAM, a "hard drive", an operating system, and a cellular modem on the serial port.

Ways to learn about how jailbreaks work

(If you're more interested in learning how to develop for jailbroken devices, such as extensions/tweaks, check out the iPhoneDevWiki instead.)

The basic idea here is that there are lots of ways to learn more about jailbreaking, for people of all experience levels and backgrounds. You might want to learn enough to actually find vulnerabilities in iOS (which is a huge undertaking), or you might just enjoy learning a little bit out of curiosity. Go through this list and pick something that looks fun to read!

Read iOS Hacker's Handbook, published in May 2012: "The award-winning author team, experts in Mac and iOS security, examines the vulnerabilities and the internals of iOS to show how attacks can be mitigated. The book explains how the operating system works, its overall security architecture, and the security risks associated with it, as well as exploits, rootkits, and other payloads developed for it."